Apparatus for treating polyethylene bodies



May 22, 1956 w. H. KRElDL ,7

APPARATUS FOR TREATING POLYETHYLENE BODIES Filed March 5, 1955 2 Sheets-Sheet l MOTOIZ TrzAusmsswN \7 coouue FLLHD 56 9 coouue ROLLER SURFACE DECORATOR I5 '1! TAKE UP ROLLEK SELSYN UNIT INVENTOR: wee N52 H. KREID L,

D ECORATO 2 /'//.S AGENTS.

y 1956 w. H. KREIDL 2,746,084

APPARATUS FOR TREATING POLYETHYLENE BODIES Filed March 5, 1955 2 Sheets-Sheet 2 INVENTOR: WERNER H. KEEIDL) United States Patent APPARATUS FOR TREATING POLYETHYLENE BODIES Werner H. Kreidl, New York, N. Y., assignor to Traver Investments, Inc., Chicago, Ill., a corporation of Illinois Application March 5, 1953, Serial No. 340,562

4 Claims. (Cl. 181) The invention relates to the treatment of polyethylene bodies to render a surface thereof receptive for the transfer thereto of decorative materials, and relates more particularly to apparatus for such treatment.

This is a continuation-in-part of my application Ser. No. 71,557, filed January 18, 1949 and entitled Method for Improving the Bonding Properties of Polyethylene Plastics, now United States Letters Patent No. 2,632,921, dated March 31, 1953.

In the aforementioned patent it is explained how a polyethylene body may be treated by heating one surface without materially heating the remainder of the body, for instance by exposing the surface to a gas flame and simultaneously cooling the opposite surface.

It has been found that a short-term heating at high temperature is preferable to heating for a longer time at a lower temperature. The high-temperature heating may for instance be accomplished by means of directing the hot portion of a gas flame into physical contact with the surface, or at least very close to the surface, or directing to the surface a blast of hot air. It appears that treating results may be achieved by the presence of oxygen during the heating, for instance by the use of an oxidizing flame or the blast of an oxygen-carrying gaseous substance.

In order to provide for short-term high-temperature heat application to any one area of the Surface of the polyethylene body, it has heretofore been thought necessary to provide for relatively high-speed relative movement between the sheet surface and the heater. For instance, it has been found that the faster the moving speed, the more uniform the treatment, and the more free will be the surface of spot defects, such as burned-through areas known in the trade as fish eyes. Such defects apparently are caused by the high temperature of the heating, and their occurrence apparently is prevented when the heat application to any given area of the surface is but brief.

In treating large-size sheets of polyethylene bodies on the production line, it has been found advantageous to use a stationary heater and to reel the sheet so that the surface will be moved past the heater for treatment. However, the fast moving of polyethylene, for instance of sheet bodies, and especially of film and flat tubing, requires expensive handling machinery and winding apparatus adapted to avoid stretching and tearing of the polyethylene material, and the expense may become prohibitive if it is made to operate at high speed for fast moving of the polyethylene material.

The instant invention has among its principal objects to provide for short-term high-temperature heating of surface areas of polyethylene bodies applied in spite of only slow relative movement between the heater and the body. Generally, this is accomplished by applying heat intermittently, instead of continuously, to successive areas of the surface.

In accordance with my aforementioned patent, the heating of one surface is coupled with the cooling of the "ice opposite surface. However, the present invention may render it possible to dispense with the necessity of cooling the reverse side. The heat impact can be made so short and so intensive that there is no heat penetration in great depth, and hence the heated surface will be treated without a material heating of the remainder of the polyethylene body.

With the above and other objects of the invention in view, the invention consists in the .novel methods, construction, arrangement and combination of various devices, elements and parts, as set forth in the claims hereof, certain embodiments of the same being illustrated in the accompanying drawings and described in the specification.

In the accompanying drawings,

Fig. 1 is a schematic elevational view of an apparatus in accordance with one embodiment of the invention;

Fig. 2 is a fragmentary perspective view, showing a detail of the heater illustrated in Fig. 1;

Fig. 3 is a fragmentary elevational view of a polyethylene sheet treated in accordance with the invention;

Fig. 4 is a schematic view similar to Fig. 1 but embodying a modification;

Fig. 5 is a schematic view similar to Fig. 1 but embodying a further modification;

Fig. 6 is a schematic view of a further embodiment;

Fig. 7 is a schematic view similar to Fig. 1, partially, however, in perspective, and embodying ,a still further modification;

Fig. 8 is a schematic view of the type of Fig. 1 but showing a modified apparatus; and

Fig. 9 is a perspective view showing a further modified apparatus.

Generally speaking, the intermittent action of the heater may be brought about by various means, some of which by way of illustration will now be exemplified below.

R0tati0n-parallel.The heater may be rotated, for instance about an axis parallel to the sheet surface and transversely of the direction of sheet movement, as it passes the heater, so that periodically the slow moving sheet will receive heat application, and in the intervening interval no heat will be applied.

A first exemplification of the rotational type of heater is shown in Figs. 1 and 2. A body 11 of polyethylene material, such as a sheet, is suspended between a takeofl? roller 12 and a take-up roller 13. Intermediate these rollers there is provided a treating station generally indicated at 14, and there may also be provided a surface decorating station 16, for instance a printing unit or label application unit or the like. In practice, the take-up roller 13 may be incorporated into the surface decorating station 16, but for the purpose of clarity, the take-11p roller 13 is shown separately. The reeling of the sheet 11 may be accomplished by driving the take-up roller 13. In the exemplification of Fig. 1, a motor 17, preferably of the speed regulatable type, is shown connected to the take-up roller 13 by a drive such as a V-belt 18 suspended between a pulley 19 of the motor 17 and a pulley 21 of the take-up roller 13.

As explained in my aforementioned patent, the front surface 22 of the sheet 11 is subjected to heating, while the rear surface 23 may be subjected to cooling. In the exemplification of Fig. 1, the sheet 11 passes over a freely rotatable roller 24, the interior of which may be cooled by a cooling fluid that is circulated therein by means of a pipe 26. As the sheet 11 is reeled, its rear surface 23, along an arcuate portion, will make contact with the surface of the roller 24, and will turn the roller 24, and will be cooled by the roller 24.

As explained in the preamble hereof, practicing of heat treating with the instant invention may dispense with 'of the sheet 11 will increase.

the necesssity of a specific cooling action. For this reason, the roller 24 may, in accordance with the instant invention, be without cooling fluid and not perform any specifiocooling action. In line with this, the cooling pipe 26 has been omitted from the subsequent views of the drawings.

Opposite the roller 24 there is positioned the heater, for instance a gas heater 27 having a plurality of burner nozzles 28. In the heat transferring position, shown in Fig. 1, the nozzles 28 will be positioned radially of the axis of the roller 24. The tips of the nozzles 28 in the treating instant as shown in Fig. 1, may be so positioned that the flame jets 29 either impinge upon the :front surface 22. of the polyethylene sheet 11 or are close enough to it to provide for treatment exposure.

The nozzles 28 will be so distributed throughout the width a of the sheet 11 that an entire transverse area of the sheet 11 will be heated by the flames 29 when the heater 27 is in the position shown in Fig. 1. A series of such areas are shown in Fig. 3 and designated there I, II, III, IV and V. The flame 29 of each nozzle 28 is sufiiciently wide to overlap in part the flame of the immediately adjacent nozzles 28, so that throughout the width of each area there will be continuous heat application free from any untreated spots.

The heater 27, as best shown in Fig. 2, is revoluble about an axis that is parallel to the axis of the roller 24, and thus perpendicular to the direction A of sheet movement as it passes the heater; the heater may be provided with journal bearing supports 31. It may revolve either in the same direction as the roller 24 (with the sheet), or opposite thereto (against the movement of the sheet 11). A stufling box 32 of conventional design may be arranged between the gas delivery pipe 33 and .the heater 27 to provide for uninterrupted sealed intercommunication during rotation of the heater 27.

The motor 17, in addition to rotating the take-up roll- 5 er 13, also is in driving connection with the heater 27.

Such a connection may'again be made by a belt drive 34 that may deliver the rotational momentum to a transmission 36 and from thereover another belt drive 37 to ithe pulley 38 of the rotatable heater 27. The rotation of the heater 27 is proportional to the rotation of the takeup roller 13, and the transmission 36 is installed to provide for adjustment of the rotational speed of the heater.

The rotational speed of the heater 27 should be so adjusted that as the flame jets 29 impinge upon, or transmit iheat by radiation to, the sheet 11, they will heat one of the areas, for instance the area I, and during the next rotation will heat the area II, and thus during each succeeding rotation, heat a subsequent area of the surface 122 of the sheet 11.

' Instead of having a direct physical driving connection to the heater 27, the motor 17 may, as shown in Fig. 4,

drive an electric synchronous torque unit such as a unit known under the trade designation Selsyn unit 41 which drives a similar Selsyn unit 42 that drives the heater 27 by means of a gear train 43. An adjustment element 44 may be provided for adjustably changing the rotational speed imparted to the heater 27.

' the cycle frequency of rotation of the heater 27 should be substantially proportional to the linear speed of the sheet 11. This arrangement permits to make the heated areas I, II V overlap each other for a portion 47, to assure that throughout the heating the entire surface 22 will be heated, and no spots be omitted.

In the exemplifications illustrated in Figs. 1, 2 and 4, the drive for rotating the heater 27 is made in relation to the rotation of the take-up roller 13. However, as the sheet 11 is rolled up on the roller 13, the linear speed Although owing to the small thickness of the sheet as compared with the diameter of the take-up roller 13, this change in linear speed of the sheet 11 is only small, adjustment may be made, for instance by means of the transmission 36 or the element 44.

In the modification shown in Fig. 5, the rotation of the heater 27 is made in a more direct manner dependent from the linear speed of the sheet 11. This may be accomplished, for instance, by securing to the roller 24 a gear 48 that is in driving connection with a gear 49 that turns the heater 27 (for instance by means of an intermediate pinion 51 and bevel gears 55). Proper selection of the pinion 51 will permit to impart to the heater 27 the desired number 'of revolutions in comparison to the linear speed of the sheet 11.

R0ration-perpendicular.-Instead of turning the heater about an axis transverse of the direction of movement of the body 11 relative to the heater, the latter may be turned about an axis parallel to that direction.

Such an arrangement is shown in Fig. 6. A band 611 is suspended between two rollers 612 and 613, and may be either a narrow sheet of polyethylene material, or a lay-flat tubing of that material, or a coated wire; or it may be a conventional conveyor band transporting polyethylene articles such as bottles or the like (not shown). The heater 627 turns about an axis that is substantially parallel to the direction A of the band 11 as it passes the heater 627. The motor 17 drives the band 11, and a separate, second motor 50 drives, by way of a transmission 636, the heater 627. The motors 17 and 50 are so arranged that the cycle of frequency of rotation of the heater 627 is proportional to the linear speed of the band 11 in direction A.

The heater 627, when used with a narrow polyethylene sheet, may have but a single pinpoint flame that sweeps transversely over the material 11, thereby creating a treated area and during the subsequent revolution a succeeding area, of the type shown in Fig. 3.

The operation of the above described embodiments is as follows.

The body 11 is suspended between the rollers 12 and 13 and either applied with its rear surface 23 against the surface of the roller 24, by means of two idlers 25 (Figs. 1-5), or be suspended (Fig. 6). The motor 17 is hooked up for driving connection with the take-up roller 13 and the heater 27 (Figs. 1 and 2). The rotary speed of the heater is adjusted in relation to the linear speed, which is the take-up speed, of the sheet 11 which, in turn, will be calculated from, and be made in dependency of, the heat of the flames 29. Thereafter, gas is admitted to the heater 27, and ignited, and the motor 17 is started.

Instead of using burning gas, hot air may be fed to the heater 27 through the feeding pipe 33.

In accordance with the embodiments of Figs. 4 and 5, the motor is not mechanically connected to the heater 27, but instead may be connected by a torque unit 42 (Fig. 4), or, further still, the roller 24 may be connected for driving to the heater 27 by means of a gear train 48, 49 and 51 (Fig. 5).

Still further, a separate motor 50 may drive the heater 637 (Fig. 6), through it will be so arranged that the frequency of the treatment pulses of exposure from the heater is proportional to the linear speed of the band 11.

The heater may rotate so that the surface moves with the body 11 or against the same (Fig. l), or transversely thereto (Fig. 6).

Speed within cycle.In the foregoing, it has been assumed that the heater 27 rotates with uniform speed. However, it may be advantageous to retard the heater during a portion of the full cycle in which it transfers heat to the sheet 11, and conversely to accelerate it during the remainder of the cycle, or vice versa. This may be accomplished, for instance, by a suitable cam or similar speed-changer arrangement within the transmission 36 or by any other suitable well-known mechanism; likewise,

. 3 4 the torque unit 42 may be so adjusted by the adjustment element 44 to provide for such non-uniform rotation of the heater 27, or the gear train 43 be changed to provide for a suitable cam or similar action (not shown).

Instead of driving the heater 27 from the motor 17, or from the train 48, 49, 51 which in turn is driven from the sheet 11, each of the heaters illustrated in Figs. 1-5 may be driven directly or indirectly by a separate motor (in the manner shown in Fig. 6) in such a way that the frequency of cycle of the heater is proportional to the linear speed of the sheet 11.

Treatment in accordance with the embodiments described hereinabove, will result in a pattern of overlapping adjacent areas I, II V, shown in Fig. 3 and thus, as the operation proceeds, the entire surface 22 of the sheet 11 will be heated, without materially heating the remainder of the sheet 11. Cooling may be applied to the surface 23 by the roller 24, to a comparably low temperature, for instance, of about 68 F. to 122 F.

Reciprocation.Instead of rotating the heater 27, the instant invention alternatively provides for the arrangement of the gearing for instance in the transmission 36 (Fig. 1), in any conventional, suitable way in such a manner that the heater 27 will oscillate for instance for an angle of 30 above and below the gap 46, thereby transferring heat intermittently to areas of the front surface 22 of the sheet 11.

The drive may be so arranged that the heater 27 moves faster during the downward stroke with the sheet 11 as compared with the upward stroke against the sheet 11, in order to compensate for the speed differential so that the heat application will be the same during the strokes in either direction. The arrangement shown in Fig. 6 may also lend itself to oscillation instead of rotation of the heater 627 transversely of the movement of the band 11 in direction A, by suitable provision of the transmission 6-36.

The cycle frequency of the heater movement will again be proportional to the linear speed of the sheet 11.

Intermittent shielding.Instead of rotating the heater, there may be arranged a shield between the heater and the surface 22 of the sheet 11, and the shield put in position during the period of each cycle when no heat application is desired, and be withdrawn to clear the path for the heat transfer during the remainder of each cycle.

Such an arrangement is shown by way of exemplification in Fig. 7. A heater 727 is mounted stationary opposite the cooling roller 24. A reciprocably movable shield 61 is placed around the heater 727, and has transverse of the-heater axis, end plates 62. The shield 61 is open towards the rear and closed towards the front except for an aperture 63. Means are provided, for instance a solenoid 64 that operates a two-armed lever 66, for reciprocably shifting the shield 61 so that in one position the aperture 63 will be in alignment with the gap 46 between the roller 24 and the heater 727, and respectively, in a second position shown in Fig. 7, the aperture 63 will be out of that alignment so that the solid portion 67 of the shield 61 will restrain heat transfer from the heater 727 to the sheet 11.

Means are provided, such as for instance a mechanism generally indicated at 68, for actuating the solenoid 64, at an actuation frequency for each complete cycle for the aperture 63 proportional to the linear speed of the sheet 11. The mechanism 68 comprises a disc 69 that is driven from the sheet 11, for instance by frictional rolling contact therewith. The disc 69 has a series of holes 71 disposed along a concentric circle, and a light projector 72 is positioned on one side of the disc 69 in alignment with the circle of the holes 71, and on the other side of the disc 69 in alignment with the projector 72 there is positioned a photoelectric cell 73. The photoelectric cell 73 is electrically interconnected to the solenoid 64, for instance over an amplifier 74 that is powered from a network.

Movement of the sheet 11 in direction 76 will rotate the disc 69, and the holes 71, in succession, will come into alignment with the light beam 77 of the projector 72. Every time that the light beam 77 is picked up by the cell 73, the solenoid 64 will be actuated and the solenoid will move the shield 61 to bring the aperture 63 into heat transfer position in the gap. After a hole 71 has passed the beam 77, the beam will be interrupted and current to the solenoid 64 will be cut off, and the shield be returned to the position shown in Fig. 7. A spring 78 may be provided to aid in the return shifting of the shield 61.

The disc 69 is rotatably journalled in a pivoted frame 79 that is urged by a spring 81 to maintain the disc 69 in rolling contact with the sheet 11. -Alternatively, rolling contact may' also be made with the lateral extension of the roller 24 beyond the width a of the sheet 11 (see Fig. 2).

Various discs 69 may interchangeably be journalled in the frame 79, in order to vary the frequency of the impulses, as well as the length of heat transfer as compared to the length of non-transfer in each shield oscillation cycle. In order to vary the frequency, the pitch between adjacent holes 71 may be changed for different discs 69. In order to vary the length of heat transfer, the holes 71 may be lengthened or shortened arcuately, peripherally of the circle on which the holes 71 are arranged, for diiferent discs 69.

The heater 727 may again be a gas burner, or deliver a blast of hot air, or be of any other suitable construction, for instance electrical, capable of delivering an oxidizing heat energy to the surface 22 of the sheet 11.

Intermittent cut-0fi.The desired result may also be obtained by intermittently connecting and respectively disconnecting the heater from its source. This may entail either complete connection and disconnection, or switching between maximum and minimum positions wherein at maximum position the heater transmits heat sufiicient for treating and at the minimum position the heater transmits only a very small amount of heat insufiicient for treatment.

An on-oif arrangement, by way of exemplification, is shown in Fig. 8. The heater or burner 827 is again assumed to be a gas flame burner, and receives gas from a delivery pipe 82. A cut-off mechanism 83 is provided in the pipe 82 and comprises a pocket 84 in which there is vertically movable a wedge 86 that has an opening 87. The wedge 86 is driven by a solenoid 88 that is in circuit with an electric source 89 and a switching device 91. When the solenoid is actuated, the opening 87 will permit passage of the gas to the burner 827, and when the solenoid 88 is released, the solid part of the wedge 86 will block the path of the gas in the pipe 82.

A motor 17 is again arranged for driving the take-up roller 13 of the sheet 11, and the motor 17 also drives a movable contact terminal 92, which forms a part of the switching device 91. An arcuate bar 93 is interconnected in said circuit, and when the terminal 92 during a portion of each turn makes sliding contact with the bus bar 93, the solenoid 88 will be energized.

Changing the length of the bus bar 93, provides for variation of the apportioning of heat transfer as against non-transfer. By providing suitable gearing (not shown) for the terminal 92, the cycle frequency of the turning on and off of the gas may be adjusted in relation to the linear speed of the sheet 11.

By operating the motor 17, the sheet 11 will be transported and the terminal 92 be rotated. When contact is made between the bus bar 93 and the terminal 92, the solenoid 88 will move the wedge 86 into the position shown in Fig. 8 wherein the opening 87 clears the passage of the pipe 82. Upon interruption of the sliding contact, the solenoid 88 will move the wedge 86 upwardly so that the solid portions thereof will block the passage for the gas.

Where maximum-minimum switching is desired, the solenoid 88 may be so set that the wedge 86 is only partially moved andthe flame be not fully turned off during the periods of minimum.

In Fig. 9, there has been shown an exemplification of an apparatus for treating a bottle 101 of the polyethylene type. An annular gas burner heater 9-27 surrounds the bottle 101 and directs its flames inwardly towards the outer surface of the bottle, either impinging it or radiating heat towards it. The bottle is stationed on a horizontal support that is moved vertically downwardly on a moving mechanism 102, which includes a rod 103 that carries a rack 104. Themovement of the rod 103 drives a mechanism 106 that operates the intermittent action of the heater 927. In this particular exemplification, the mechanism 106 has been patterned somewhat on that shown in Fig. 8, and which comprises an electric circuit 107 to cut in-and-out a wedge 986 from the feed pipe 982 for the gas. The rack 104 drives a pinion 108 that carries a rotatable sliding contact 992 which cooperates with a bus bar 9--93 to energize and respectively to de-energize a solenoid -88 from a source 989. In all other respects, the operation of the embodiment shown in Fig. 9 is similar to that described in connection with Fig. 8.

The bottle 101 may, if desired, be cooled on the interior, either by a cooling fluid or a cooling liquid.

Specific sample data.-By way of exemplification only, and not in any limiting sense, the following data are given. Where a gas burner is used, the heat developed by the flame, may be such that the front surface of the polyethylene body 11 is elevated to a temperature of from 600 to 700 F. or more. The distance between the tips of the burner and the front surface of the body 11 may be so varied, and the length of the flame jets be so adjusted that in the nearmost position the oxidizing portion of the flame either impinges directly upon the surface or is spaced for a predetermined small distance therefrom, for instance up to one inch.

The linear transporting speed of the body 11 may be from 60 to 100 feet per minute, and the heater may rotate or oscillate with a peripheral nozzle speed so that the nozzle has a linear differential speed as against the body 11 of from 400 to 500 feet per minute. means that, when the flame travels with the sheet, the heater rotation must be faster than when the flame travels opposite to the body 11.

Where a blast of hot air is used, the temperature of the hot air may be 2000 F. or more.

The instant invention permits the use of very hot flames which heretofore could not be used in connection with polyethylene bodies. Such very hot flames may be provided by means of oxygen torches, oxygen acetylene burners and similar supercharged heaters. The intermittent action permits to avoid the drawbacks usually attendant in connection with polyethylene heating when very hot flames are employed; It also permits that separate cooling of the opposite surface of the body 11 may be omitted. It will be apparent to those skilled in the art that the This novel principles ofthe invention disclosed herein in connection with specific exemplifications thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the spe cific exemplifications of the invention described herein.

Having thus described the invention, what I claim as new and desire to'be secured by Letters Patent, is asfollows: 1. In an apparatus, for use in treating a body of polyethylene to render a surface thereof receptive for the transfer of decorative material, in combination, a support for suspending said body, a heater operatively positioned for transmitting heat to said surface, means actuable for movement of said surface relative to said heater to expose succeeding surface areas to the heat transmission, said heater being pivoted for movement about an axis substantially parallel to said surface when the latter is opposite said heater, and a mechanism for turning said heater about its axis, at a cycle frequency substantially proportional to the speed of said movement, whereby continuous areas of said surface will intermittently be heated during spaced time intervals of said movement and, respectively, said surface will be free from heat application during the intervening time intervals and each succeeding heated area will overlap for a portion a preceding heated area.

2, In an apparatus, as claimed in claim 1, said axis of said heater being positioned substantially parallel ofthe direction of said movement.

3. In an apparatus, as claimed in claim 1, together with, said moving means being in driving connection with said mechanism for timed turning of said heater.

4. In an apparatus, for use in treating a body of polyethylene to render a surface thereof receptive for the transfer of decorative material, in combination, a support for suspending said body, a heater operatively positioned for transmitting heat to said surface throughout a continuous area thereof, means actuable for movement of said surface relative to said heater to put in registry with said heater succeeding continuous surface areas, said heater being revoluble about an axis parallel to said surface in registry, and a mechanism for rotating said heater at a cycle frequency substantially proportional to the speed of said movement, whereby continuous areas of said surface will intermittently be heated during spaced time intervals of said movement and, respectively, said surface will be free from heat application during the intervening time intervals and each succeeding heated area will overlap for a portion a preceding heated area.

References Cited in the file of this patent UNITED STATES PATENTS 2,355,391 Nelson et al Aug. 8, v1944 2,511,024 Toulmin June 13, 1950 2,551,005 Johnson May 1, 1951 2,576,317 Toulmin Nov. 27, 1951 2,632,921 Kreidl Mar. 31, 1953 2,648,097 Kritchever Aug. 11, 1953 

1. IN AN APPARATUS, FOR USE IN TREATING A BODY OF POLYETHYLENE TO RENDER A SURFACE THEREOF RECEPTIVE FOR THE TRANSFER OF DECORATIVE MATERIAL, IN COMBINATION A SUPPORT FOR SUSPENDING SAID BODY, A HEATER OPERATIVELY POSITIONED FOR TRANSMITTING HEAT TO SAID SURFACE, MEANS ACTUABLE FOR MOVEMENT OF SAID SURFACE RELATIVE TO SAID HEATER TO EXPOSE SUCCEEDING SURFACE AREAS TO THE HEAT TRANSMISSION, SAID HEATER BEING PIVOTED FOR MOVEMENT ABOUT AN AXIS SUBSTANTIALLY PARALLEL TO SAID SURFACE WHEN THE LATTER IS OPPOSITE SAID HEATER, AND A MECHANISM FOR TURNING SAID HEATER ABOUT ITS AXIS, AT A CYCLE FREQUENCY SUBSTANTIALLY PROPORTIONAL TO THE SPEED OF SAID MOVEMENT, WHEREBY CONTINOUS AREAS OF SAID SURFACE WILL INTERMITTENTLY BE HEATED DURING SPACED TIME INTERVALS OF SAID MOVEMENT AND, RESPECTIVELY, SAID SURFACE WILL BE FREE FROM HEAT APPLICATION DURING THE INTERVENING TIME INTERVALS AND EACH SUCCEEDING HEATED AREA WILL OVERLAP FOR A PORTION A PRECEDING HEATED AREAS. 